1. Field of the Invention
This invention relates to a mold clamping mechanism useful on a tire curing press for clamping upper and lower molds during tire vulcanizing operation, and more particularly to a mold clamping mechanism of a stable and sturdy construction which can maintain a high degree of concentricity and parallelism of upper and lower molds in a facilitated manner.
2. Description of the Prior Art
As well known in the art, for vulcanizing to shape a green tire which has been placed in upper and lower molds of a tire curing press, it is necessary to clamp the upper and lower molds in a closed state against a high internal pressure which develops within the molds. In this regard, there have been used various conventional or improved mold clamp means. In a typical conventional mold clamp mechanism, opening and closure as well as clamping of an upper mold relative to a lower mold is attained by upward or downward movement of a main beam on which the upper mold is mounted, lifting the main beam up and down by a side link which is operated by a crank gear, a cam groove and so forth and mounted on side plates provided on opposite sides of the tire vulcanizing press. The use of this sort of conventional tire clamp mechanism generally results in a disadvantageously large increase in size and complication in construction, coupled with an inferior press efficiency and possibilities of imperfect alignment of closed upper and lower molds due to flexure of the main beam. Above all, it has been a great problem for the conventional mold clamping mechanism to comply with the requirement that the concentricity and parallelism of the upper and lower molds should be strictly maintained at the time of mold closure and clamping in a tire curing operation.
In place of the above-mentioned conventional mold clamp mechanism, there have been employed in the art improved mold clamp mechanisms which are provided with a mold pressing means separate from a mold lift means which serves to open and close upper and lower molds, and in which the molds are opened and closed by vertically moving an upper mold up and down relative to a lower mold on a press base, clamping the upper and lower molds directly by a pressing means which is provided in the vicinity of the molds to generate a mold clamping force. Although there are various types of improved mold clamp mechanisms, it would be appropriate here to take a recent example which is provided with a press base having a lower mold cavity fixed thereon; a lower mold assembly received in the lower mold cavity and including a platen support, a heat insulator, a platen, and a mold, the lower mold assembly being vertically movably supported by a hydraulic cylinder which is mounted on a lower portion of the press base; and an upper mold cavity supported on a vertically movable beam and incorporating therein an upper mold assembly opposed to the lower mold assembly. After closing and locking the upper mold cavity on the lower mold cavity, the lower mold assembly is lifted up and clamped against the upper mold assembly by the hydraulic cylinder.
The above-described type of improved mold clamp mechanism has certain advantages such as utilizing a relatively short stroke length of the hydraulic cylinder, simplifying to some extent an upper mold support structure which is free of the reaction of mold clamping force, and simplifying and reducing the size and cost of the curing machine as a whole. However, on the contrary, a mold clamp mechanism of the type which has a lower mold assembly vertically movably mounted on a press base has a serious problem regarding the concentricity and parallelism of upper and lower mold assemblies which are the most important factors to be considered in the tire curing operation and failing to attain a high degree of alignment of the upper and lower molds which is essential to improving the quality of the ultimate products. Besides, regarding simplifications in construction and maintenance which have thus far been strongly demanded, it becomes necessary to mobilize the heat source for the movable lower mold, for example, to provide a movable support structure for a steam pipe by the use of a rotary joint, a flexible tube or the like, inviting as a result further problems such as complication in construction, damage of component parts by repeated reciprocal movements and fortification of seal construction.